Raman signatures of charge ordering inK0.3WO3

Abstract

We present polarization-and temperature-dependent Raman spectroscopic study of hexagonal tungsten bronze, K 0.3 WO 3 . The observed asymmetry in phonon line shapes indicate the presence of strong lattice anharmonicity arising due to the nonstoichiometry of the material. We observed a broad multipeak Raman feature at low frequency due to the local modes of K atoms known as local structural excitations. The observed vibrational features indicate a second-order phase transition around T = 200 K accompanied by a frequency softening of low-frequency phonon modes. The observed phonon anomalies hint a physical picture involving a continuous symmetry change toward a charge-ordered state below 200 K. These observations indicate that K 0.3 WO 3 may exhibit a weak charge-density-wave ground state at low temperatures.

Temperature dependence of phonon spectra and structural characteristics in multiferroic LuFe2O4 system

“…In the 2D ordered state, the long‐range charge‐ordering along c ‐axis is destroyed 14. The disorder leads to the enhancement of the Raman intensity,37 so the increase of the intensity of $A_{\rm {1g}}^{3}$ is probably due to the decrease in the degree of the FeO interlayer ordering. However, at temperatures below T CO , the intensities of all the modes increase as the temperature further decreases, which may be also due to the competition between the two factors mentioned previously, i.e.…”

Quantum Confined Electron–Phonon Interaction in Silicon Nanocrystals

“…In solid systems, such symmetry breaking modes typically arise from disorder. 18 In the RWL model the observed frequency redshift (with respect to the bulk LO energy) for smaller NCs is governed by the phonon dispersion. In contrast, some researchers have ascribed the asymmetry on the low frequency side to interface states associated with a disordered surface 13 where bond lengths and angles can vary from the crystalline core.…”

Characterization of K6Ta10.8O30 Microrods with Tetragonal Tungsten Bronze-Like Structure Obtained from Tailings from the Penouta Sn-Ta-Nb Deposit

“…As for the starting material, EDX analysis has been performed, showing the same element distribution, with only a weak impurity peak associated to Al In comparison with previous literature of crystal structures with similar units [17][18][19][20][21][22], we can divide the Raman spectrum into four different frequency regions: low (ν < 100 cm −1 ); medium-low (100 cm −1 < ν < 450 cm −1 ); medium-high (450 cm −1 < ν < 900 cm −1 ); and high (ν > 900 cm −1 ). In the ν < 100 cm −1 region, the modes associated with the vibrations of the K-O bonds are found, since K ions are loosely bounded to the oxygen atoms surrounding the tunnel and the long bond distance [7,23]. In the rest of the frequency regions, most of the observed bands can be related to the internal modes of TaO 6 polyhedra.…”

“…In the medium-low and medium-high frequencies, the bending and stretching vibrations of the TaO 6 polyhedra are found. As the stretching modes usually appear at higher frequencies than the bending modes, the 100 cm −1 < ν < 450 cm −1 would correspond to the bending related modes of the TaO 6 octahedra, Ta-O-Ta bending modes appearing at the lower frequencies of this range, while at the higher frequencies the O-Ta-O bending modes would be found [20,23]. It has also been proposed that the band around 200 cm −1 could have some contribution from TaO 6 -K bond modes [24].…”